Variable capacity lift truck

ABSTRACT

An industrial truck includes a shiftable counterweight for stabilizing the truck under various loading conditions. Means are provided for automatically shifting the counterweight in response to the load being supported by the lifting mechanism of the industrial truck and wherein the magnitude of counterweight movement is proportional to the magnitude of said load to thereby automatically position the counterweight for balancing the load.

United States Patent [191 Esser [451 May 22,1973

[54] VARIABLE CAPACITY LIFT TRUCK [75] Inventor:

[73] Assignee: Eaton Corporation, Cleveland, Ohio [22] Filed: July 15,1971 [21] Appl. No.: 162,894

Ernst S. Esser, Levittown, Pa.

[52] US. Cl ..214/674, 214/142 [51] Int. Cl. .3661 9/20 [58] Field ofSearch ..212/48; 214/127, 214/142, 672, 673, 674, 762, 763, 764; 91/412,433

[56] References Cited UNITED STATES PATENTS 2,759,563 8/1956 Marnon eta1. ..214/672 3,266,636 8/1966 Dom ..2l4/l42 2,460,774 2/ 1949 Trautman..91/4l2 2,266,921 12/1941 Trautman..... ..9l/412 2,926,799 3/1960Granryd ..2l4/142 Primary Examiner--Gerald M. Forlenza AssistantExaminer-Lawrence J. Oresky Attorney-Leslie H. Blair et al.

[5 7 ABSTRACT An industrial truck includes a shiftable counterweight forstabilizing the truck under various loading conditions. Means areprovided for automatically shifting the counterweight in response to theload being supported by the lifting mechanism of the industrial truckand wherein the magnitude of counterweight movement is proportional tothe magnitude of said load to thereby automatically position thecounterweight for balancing the load.

6 Claims, 2 Drawing Figures 1 VARIABLE CAPACITY LIFT TRUCK BACKGROUND OFTHE INVENTION 1. Field of the Invention The present invention relates toindustrial trucks of the type having a counterweight which is movablefor varying the capacity of the truck.

2. Description of the Prior Art The most pertinent examples of prior artknown to the applicant are U.S. Pat. No. 2,711,227, issued to W. L.Shimmon; U.S. Pat. No. 2,916,172, issued to B. H. Locke; U.S. Pat. No.3,490,622, issued to Brackin; and U.S. Pat. No. 3,504,933, issued toAvis et al. All of these patents disclose an industrial truck having acounterweight which is shiftable to increase the load carrying capacityof the: truck associated therewith. However, in all of theaforementioned patents except the Locke patent, actuation of the meansfor shifting the counterweight must be the result of a conscious manualact on the part of the truck operator. In these patents, an operatormust manually actuate a valve or some other device in order to positionthe counterweight for most efficient operation of the truck. Thus, itshould be evident that these types of arrangements are subject to humanerror and could result in a dangerous condition if the operator of thetruck were to be careless in his adjustment of the counterweightpositioning mechanism.

The Locke patent discloses a device which may be either manuallyactuated by the operator or automatically actuated by a mercury switchif the vehicle is tilted due to an attempt on the part of the operatorto cause the truck to lift a load which is beyond the capacity of thelift truck with the counterweight in its then present position. However,this system also has certain obvious disadvantages. First, it should benoted in the Locke patent that no provision is made for automaticallyreturning the counterweight to the position for most efficient operationwhen the truck has been unloaded. Secondly, the lift truck must betilted or pivoted about the front axis into an unstable position beforethe mercury switch will actuate the counterweight positioning mechanism.Furthermore, it would appear that if the lift truck were operated overrough surfaces, as are frequently encountered in the use of industrialtrucks, the resultant jostling and bumping could cause the mercurywithin the switch to continually actuate and deactuate the counterweightpositioning mechanism resulting in an unstable condition during movementof the truck by shifting of the counterweight and thus presenting asafety hazard.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an industrial truck having a balanced counterweightwhich is automatically shiftable by an amount which is a function of themagnitude of the load being lifted.

It is another object of the present invention to provide a new andimproved means for positioning the counterweight in an industrial truckand wherein the amount of counterweight movement is proportional to thepressure in a hydraulic load lifting circuit.

It is a further object of the present invention to provide an industrialtruck having a counterweight which is automatically shiftable inresponse to the lifting of a load to provide better stability of saidtruck when lifting a heavy load and wherein said counterweight isautomatically returned to the no-load position upon removal of the loadfrom said industrial truck.

To accomplish the above objective, the present invention provides anindustrial truck of the type having a counterweight which is shiftablein order to vary the capacity of said industrial truck including meansfor automatically varying the position of the counterweight in a mannerwhich is a function of the magnitude of the load on the liftingmechanism on said industrial truck.

In a preferred embodiment, a pressure tap is connected from thepressurized side of either the load lifting hydraulic rarn or the tiltcylinder of an industrial truck through a variable orifice to a pilotoperated shuttle valve. Upon the existence of a predetermined amount offorce being applied to either the lift or tilt cylinders due to theload, the pilot operated shuttle valve is actuated to connect ahydraulic cylinder attached to the counterweight to a pressurizedhydraulic source. Thus, the hydraulic cylinder associated with thecounterweight may be actuated by an amount which is a function of thepressure in the tilting or load lifting cylinders of the industrialtruck. A variable orifice may be supplied in the hydraulic circuitbetween the tilt or load lifting cylinders of the industrial truck andthe pilot operated valve in order to prevent pressure surges due tooperation of the truck over a rough surface, thereby preventinginadvertent actuation of the pilot operated valve. In addition, a secondpilot is connected to allow fluid flow out of the counterweight cylinderwhen the pressure within either the tilt or load lifting cylinders ofthe industrial truck falls below the pressure in the counterweightcylinder.

Other objects and advantages of the present invention will become moreapparent from a reading of the detailed description of the preferredembodiment which follows hereinafter.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of anindustrial truck incorporating the mechanism of the instant invention.

FIG. 2 is a schematic hydraulic circuit disclosing one method ofincorporating the instant invention into an industrial truck.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 1, thereis shown a standard industrial truck 10 having a pair of forks 12 or thelike for lifting a load as shown in phantom. The forks 12 carrying theload are adapted to be raised and lowered in a standard manner along themast 13 by means of a hydraulic cylinder (not shown) under the controlof a vehicle operator. The industrial truck further includes a tiltcylinder 14 pivotally attached between the mast 13 and the frame of theindustrial truck for tilting the mast under the control of a vehicleoperator in a standard manner well-known in the art, thereby moving theoperator and further that the mast 13 may be tilted toward or away fromthe main frame of the industrial truck. Although the means forautomatically adjusting the position of the counterweight of the instantinvention could be used in conjunction with the pressure in the loadlifting mechanism of the industrial truck, for purposes of the preferredembodiment of the present invention, automatic operation of thecounterweight positioning means has been connected to be operated inresponse to pressure in the tilt cylinder 14. It should be noted thattilting of the mast 13 will pivotally raise and lower the load on theforks 12 relative to the industrial truck 10.

In the instant invention, a conduit 16 has been connected from thepressure side of the tilt cylinder 14 to a pressure responsive controlmechanism 18. The pressure responsive control mechanism 18, is in turnconnected by means of a conduit 20 to a second hydraulic cylinder 22pivotally attached to the frame of the vehicle by means of a pivot pinconnection 23 as shown in FIG. 1. A piston rod 24 of the hydrauliccylinder '22 is in turn connected by means of a pivot pin connection 25to a movable counterweight 26 disposedat the rear of the industrialtruck as shown in FIG. 1. The counterweight 26 is in turn pivotallysupported on the frame of the industrial truck by means of a boss 28having a pivot pin 30 passing through both the boss 28 and thecounterweight 26. Although the counterweight 26 could be mounted on theindustrial truck in many various ways, such as sliding rails or thelike, for purposes of the preferred embodiment, the pivotal connectionsupplied between the boss 28 and the pivot pin 30 has been used.

The control mechanism 18 has been supplied with conduits 32 and 34 foradapting the control mechanism 18 to be connected to the normalhydraulic circuit of the industrial truck 10. One of the conduits 32 isthereby adapted to provide pressurized fluid to the control mechanism18, while the other conduit 34 is adapted to return hydraulic fluid fromthe control mechanism 18 to the reservoir of the industrial truck allwhich will be well understood by those skilled in the art to which thisinvention pertains.

Referring now to FIG. 2 wherein there is shown a schematic hydrauliccircuit incorporating the mechanism of the instant invention for a morecomplete understanding of the hydraulic connections and apparatus withincontrol mechanism 18 which may used to accomplish the objects of thepresent invention.

FIG. 2 shows in schematic the tilt cylinders 14 of the industrial truck10. The tilt cylinder 14 is connected by means of the conduit 16 tocontrol mechanism 18 for providing a pressure signal to actuate controlmechanism 18. Upon actuation of control mechanism 18, fluid will flowthrough conduit 20 to pressurize the second hydraulic control cylinder22 thereby moving the counterweight 26 pivotally attached to the frameof the industrial truck as described above.

The automatic hydraulic control mechanism 18 includes a three-position,four-way closed center valve 40. The valve 40 is a pilot operated,spring centered shuttle valve having a first pilot 42 and associatedspring 44 and a second pilot 46 and associated spring 48. The springs 44and 48 are effective to maintain the spool of the valve 40 in the centeror closed position when no pressure exists on either of the pilots 42 or46. The pilot 42 is connected by means of conduit 16 to the cylinders14. Conversely, pressure actuated pilot 46 is connected by means of aconduit 49 internally of the control mechanism 18 to sense hydraulicpressure in conduit 20, thereby adapting pilot 46 to move the spool ofshuttle valve 40 to the left as shown in FIG. 2 to recenter valve 40when the proper feedback pressure is reached. The internal hydraulicconnections which result from movement of the spool of the closed centerthree-position four-way valve 40 should be evident to those skilled inthe art from the standard hydraulic representations designated by flowarrows as shown on the valve 40.

For purposes of eliminating pressure fluctuations in the pressure signalfrom tilt cylinders 14 to pilot 42 due to operation of the industrialtruck over rough surfaces, a variable orifice 50 has been incorporatedinternally of the hydraulic control mechanism 18 in the conduit 16between the rod end of tilt cylinder 14 and pilot 42.

The importance of the previously described hydraulic connections andapparatus will become more fully apparent from the description ofoperation of the preferred embodiment which follows hereinafter..

DESCRIPTION OF OPERATION Upon pressurization of the tilt cylinders 14, apressure signal passes through conduit 16 to pilot 42 thereby actuatingpilot 42 to move the spool of the shuttle valve 40 to the right againstspring 48. This movement will connect conduit 32 associated with thepressurized hydraulic system of the industrial truck to conduit 20thereby pressurizing hydraulic cylinder 22 to begin moving counterweight26. As counterweight 26 moves outwardly and upwardly, the pressure inhydraulic cylinder 22 increases thereby increasing a feedback pressurein conduit 49 communicating with pilot 46. When the counterweight 26 hasmoved outwardly and upwardly a sufficient amount, the back pressure incylinder 22 and resulting feedback pressure in conduit 49 through itsconnection with conduit 20, will cause this back pressure to actuatepilot 46 to return the spool of valve 40 to its normally centeredposition. This will shut off the flow of hydraulic fluid from conduit 32through valve 40 to the counterweight cylinder 22. Since the shuttlevalve 40 is of the closed center type, the hydraulic fluid withincylinder 42 will remain in a pressurized state maintaining counterweight26 in a position which is a function of the hydraulic pressure in tiltcylinders 14 and conduit 16.

Upon lowering of the load on the forks 32 of the industrial truck 10 andrelease of the hydraulic pressure in the tilt cylinders 14 and conduit16, the back pressure in cylinder 22 resulting from displacement ofcounterweight 26 will act on pilot 46 through conduit 49 to move thespool of the pilot operated shuttle valve 40 to the left as shown inFIG. 2. This movement will connect conduit 20 to conduit 34 therebyallowing the pressurized hydraulic fluid contained in counterweightcylinder 22 to flow back through valve 46 and conduit 34 to reservoir,thus permitting counterweight 26 to pivot downwardly and to the right asshown in FIG. 2 to its normal lowered position.

If the industrial truck to which the hydraulic circuit of the instantinvention has been incorporated is operated over a rough surface itshould be realized that the pressure in hydraulic cylinders 14 andconsequently pressure in conduit 16 will have a tendency to fluctuatedue to bouncing and jostling of the load disposed in the forks 12. Thiscould result in an uneven or jerking pres sure signal to pilot 42.Consequently, it has been found desirable to incorporate a variableorifice 50 into the hydraulic line 16 connecting to pilot 42 to therebyallow adjustment for damping out any rapid pressure fluctuations inconduit 16 and provide for smooth operation of the pilot 42 associatedtherewith.

Having thus described the invention as to enable one of ordinary skillin the art to practice the teachings disclosed herein, I now claim:

1. In an industrial truck having a load lifting member supported thereonfor movement relative thereto, said load lifting member being adapted tosupport a load thereon; a first hydraulic cylinder operatively mountedbetween said load lifting member and said industrial truck, said firsthydraulic cylinder being adapted to move said load lifting memberrelative to said industrial truck; a counterweight mounted on saidindustrial truck, said counterweight being adjustable to variouspositions for counterbalancing a load which may be supported on saidload lifting member; means automatically responsive to the hydraulicpressure in said first cylinder for adjusting the position of saidcounterweight as a function of the load on said load lifting member; andmeans for preventing the transmittal of rapid fluctuations in pressuresignal from said first hydraulic cylinder to said automaticallyresponsive means whereby said industrial truck may be operated overrough surfaces without affecting the position of said counterweight.

2. The invention of claim 1 wherein said counterweight is pivotallyattached to said industrial truck, and including a second hydrauliccylinder operably connected between said industrial truck and saidcounterweight for moving said counterweight in response to actuation ofsaid automatically responsive means whereby said counterweight may bemoved by an amount which is a function of the load on said load liftingmember.

3. The invention of claim 2, wherein said means for automaticallyadjusting the position of said counterweight comprises a pilot operatedshuttle valve having a first pilot for moving said shuttle valve in onedirection, a first conduit communicating between said first hydrauliccylinder and said pilot for actuating said shuttle valve in response topressure in said first hydraulic cylinder, a second conduitcommunicating between said shuttle valve and said second hydrauliccylinder, and a third conduit communicating between said shuttle valveand a pressurized source of hydraulic fluid on said industrial truck,whereby movement of said shuttle valve in response to actuation of saidfirst pilot will cause hydraulic fluid to flow from said pressurizedsource to said second hydraulic cylinder for moving said counterweight.

4. The invention of claim 3 including pressure damping means disposed insaid first conduit for preventing the transmittal of rapid fluctuationsin pressure signal from said first hydraulic cylinder to said firstpilot.

5. The invention of claim 3 wherein said means for automaticallypositioning said counterweight further comprises a second pilot adaptedfor moving the spool of said shuttle valve in the other direction, and afourth conduit communicating between said second pilot and said secondconduit to thereby enable said second pilot to move the spool of saidshuttle valve in the opposite direction upon the existence of apredetermined pressure relationship between said fourth conduit and saidfirst conduit.

6. The invention of claim 5 wherein said second pilot is operable inresponse to the existence of pressure in said fourth conduit higher thanthe pressure in said first conduit for moving the spool of said shuttlevalve to relieve the pressure in said second hydraulic cylinder therebyreturning said counterweight toward the initial unloaded position.

1. In an industrial truck having a load lifting member supported thereonfor movement relative thereto, said load lifting member being adapted tosupport a load thereon; a first hydraulic cylinder operatively mountedbetween said load lifting member and said industrial truck, said firsthydraulic cylinder being adapted to move said load lifting memberrelative to said industrial truck; a counterweight mounted on saidindustrial truck, said counterweight being adjustable to variouspositions for counterbalancing a load which may be supported on saidload lifting member; means automatically responsive to the hydraulicpressure in Said first cylinder for adjusting the position of saidcounterweight as a function of the load on said load lifting member; andmeans for preventing the transmittal of rapid fluctuations in pressuresignal from said first hydraulic cylinder to said automaticallyresponsive means whereby said industrial truck may be operated overrough surfaces without affecting the position of said counterweight. 2.The invention of claim 1 wherein said counterweight is pivotallyattached to said industrial truck, and including a second hydrauliccylinder operably connected between said industrial truck and saidcounterweight for moving said counterweight in response to actuation ofsaid automatically responsive means whereby said counterweight may bemoved by an amount which is a function of the load on said load liftingmember.
 3. The invention of claim 2, wherein said means forautomatically adjusting the position of said counterweight comprises apilot operated shuttle valve having a first pilot for moving saidshuttle valve in one direction, a first conduit communicating betweensaid first hydraulic cylinder and said pilot for actuating said shuttlevalve in response to pressure in said first hydraulic cylinder, a secondconduit communicating between said shuttle valve and said secondhydraulic cylinder, and a third conduit communicating between saidshuttle valve and a pressurized source of hydraulic fluid on saidindustrial truck, whereby movement of said shuttle valve in response toactuation of said first pilot will cause hydraulic fluid to flow fromsaid pressurized source to said second hydraulic cylinder for movingsaid counterweight.
 4. The invention of claim 3 including pressuredamping means disposed in said first conduit for preventing thetransmittal of rapid fluctuations in pressure signal from said firsthydraulic cylinder to said first pilot.
 5. The invention of claim 3wherein said means for automatically positioning said counterweightfurther comprises a second pilot adapted for moving the spool of saidshuttle valve in the other direction, and a fourth conduit communicatingbetween said second pilot and said second conduit to thereby enable saidsecond pilot to move the spool of said shuttle valve in the oppositedirection upon the existence of a predetermined pressure relationshipbetween said fourth conduit and said first conduit.
 6. The invention ofclaim 5 wherein said second pilot is operable in response to theexistence of pressure in said fourth conduit higher than the pressure insaid first conduit for moving the spool of said shuttle valve to relievethe pressure in said second hydraulic cylinder thereby returning saidcounterweight toward the initial unloaded position.